Field of the Invention
The present invention relates to rifle construction, firearm accessory mounts and more particularly relates to accessory mounts and methods for configuring a rifle with a modular structure for attaching accessories.
Discussion of the Prior Art
It is well known to those skilled in the art that firearms such as precision rifles and military rifles, e.g., M16 type rifles, are characterized by the heating of the barrels to relatively high temperatures. At such temperatures, the barrels cannot be safely held by the shooter. Consequently, a variety of forearms or handguards have been developed to surround and provide adequate cooling for the gun barrel and mitigate the possibility of burning the shooter's hands, as disclosed in U.S. Pat. Nos. 4,663,875 and 5,010,676.
With the continuing application of newly developed technologies, e.g., lasers, infrared ray scopes, micro-computerization, etc., to modern warfare, the basic combat weapon, i.e., rifles, carbines and shotguns, have become relatively complicated. This has resulted in requirements for the association of these weapons with a variety of accessories such as infrared and night vision scopes, laser spotters and the like. Use of such accessories has driven development of various types of mounting devices for rifles (see, e.g., U.S. Pat. Nos. 4,026,054, 4,733,489, 4,845,871, 5,198,600, 5,343,650 & 5,590,484).
Because firearms may be subjected to substantial abuse, plus the need for as much simplicity as possible in construction and use of the weapon, very serious requirements and restrictions are encountered in the development of militarily acceptable systems for mounting accessories to firearms. Many accessory devices used with rifles or carbines such as the M4 (e.g., 100, shown in FIG. 1A), require attaching a replacement for the traditional handguard 102. FIGS. 1B, 1C and 1D show attachment of a Knights Armament rail equipped handguard attachment 103 on an M-16 rifle 101, and this rail equipped handguard system 103 is described and illustrated in U.S. Pat. No. 5,826,363. The Knight Armaments rail adapter system illustrated in FIGS. 1B-1D has received widespread acceptance by providing a handguard system that incorporates four rail adapters to accept and support accessory devices. The rails 103 on the Knight rail adapter system (and others) are standardized mounting rails which are compatible with the Picatinny rail platform (MIL-STD-1913 or STANAG 2324), as illustrated in FIGS. 1E and 1F (which are taken from MIL-STD-1913 (AR), adopted on Feb. 3, 1995; the title of the publication is “Dimensioning Of Accessory Mounting Rail For Small Arms Weapons” and this document specified exactly what the dimensions and tolerances were for any mounting systems that were to be submitted for acceptance by the military).
The Picatinny rail (as illustrated in FIGS. 1E and 1F) has a cross-section shape roughly like a wide T with a planar top corresponding to the top (or outermost) surface of the rail. The rail has a number of evenly spaced transverse slots or grooves in the top spanning the width of the T-shaped cross-section, thus defining a plurality of inter-groove raised lugs having many exposed sharp corners and edges. The mounting rails 103 extend over the rifle handguard surrounding the rifle barrel and four distally extending rails (or “quad rails”) are radially spaced at 90 degrees to provide top, bottom, left side and right side mounting options all of which extend along axes which are substantially parallel to the rifle's bore. Similar mounting rails are also configured for use on shotguns and pistols.
While quad rail handguard assemblies with mounting rails 103 have obvious utilitarian benefits, they also have shortcomings. Most notably, they can be uncomfortable or cause injury when grasped by a shooter, they can snag on clothing, barbed wire or other objects, and if equipped with handplates, hand panels or other components, they add weight and complexity to a weapon system.
Other mounting systems have detachable rails that allow the user to install rails only where they are needed, and only of the length needed. While this decreases weight (and the discomfort and other disadvantages) of having needless rails where the hand is to grip, it suffers from other disadvantages. First, such systems may be difficult or complex to install. Second, they may require custom modification of parts, such as drilling and tapping holes where needed. Third, the attachment locations may be in limited locations due to the need to relocate fasteners such as threaded inserts (or may increase cost and weight by using an excessive number of fasteners). A further significant disadvantage of systems having modular rails that may be mounted in various locations on the forearm or handguard of a rifle stock is the susceptibility to loosening. If the mount for a rifle scope becomes loose, this can cause significant aiming errors. One solution to the disadvantages of Picatinny quad rail systems is the MAGPUL™ MOE™ handguard assembly described and illustrated in Magpul's U.S. Pat. No. 8,925,236, which provides a method for attaching accessory rail segments and other items to an ergonomically shaped MOE™ brand handguard. These rails and mounting attachments, once mounted, also appear to present the susceptibility to loosening.
Another approach is the KEYMOD™ system introduced by VLTOR Weapon Systems. The KEYMOD system consists of two parts: the KEYMOD slot; and the KEYMOD nut. The slot is distinctive with a larger diameter through-hole combined with a narrow slot. The slot is chamfered on the backside while the through-hole is sized for clearance of a quick-detach sling swivel (approximately ⅜″ diameter). However, the KEYMOD specifications also suffer from several disadvantages including more complex and expensive manufacturing requirements.
Precision shooters engaged in benchrest competition, Varmint hunting, military or police sniping or precision rifle match competition face additional problems relating to barrel heat management. As shots are fired, a barrel becomes increasingly hot and eventually heat rising from the barrel can cause a visible optical distortion in the shooter's view or image of the target, and this optical distortion is called “mirage.” Recreational shooters such as benchrest competitors have fashioned some novel and inexpensive mirage shields from old venetian blind strips or strips of elastically stretched fabric which extend over the upper surface of the barrel's length, and these mirage shields can, if properly installed and not disturbed, reduce or eliminate optical distortions in the target image caused by heat rising from the barrel. See, for example, http://bulletin.accurateshooter.com/2014/07/one-dollar-do-it-yourself-mirage-shield/. These shields are typically fragile and may be disturbed or stripped away altogether if carelessly handled.
Therefore, there is a need in the art for a firearm accessory mounting interface that adds minimal or no weight to a weapon system, is unlikely to snag and is comfortable to hold and which is durable and so does not require excessive care or special handling. There is also a need for a convenient, flexible, structurally rigid but ergonomically friendly and unobtrusive system and method for allowing users to attach rail-mountable accessories to a weapon such as a rifle or carbine.